Formation of letters or images on an object by a thermal transfer system has hitherto been carried out in the art. A thermal dye transfer system and a thermal ink transfer system have been extensively used as the thermal transfer system. The thermal dye transfer system is such that a sublimable dye is used as a colorant, and the dye in a sublimable dye layer provided in a thermal transfer sheet is thermally transferred onto an object, such as a thermal transfer image-receiving sheet, by means of a heating device, such as a thermal head, wherein generation of heat is regulated according to image information, thereby forming an image on the object.
In the thermal dye transfer system, the amount of the dye transferred can be regulated for each dot by heating in very short time. The image thus formed is very sharp, because the colorant used is a dye, and, at the same time, is highly transparent. Therefore, the image has excellent halftone reproduction and gradation, high definition, and high quality comparable to that of full-color photographic images using a silver salt.
A thermal transfer image-receiving sheet, for thermal dye transfer, used in the thermal dye transfer system (hereinafter referred to as "thermal transfer image-receiving sheet") generally comprises a colorant-receptive layer provided on a substrate layer. Properties required for the image-receiving sheet include not only high sensitivity in printing but also minimized electrification (electro static charge) during printing by means of a printer. Electrification of the image-receiving sheet by static electricity results in deposition of dust on the surface of the image-receiving sheet or generation of cockling in a thermal transfer sheet which comes into contact with the thermal transfer image-receiving sheet, posing a problem that the appearance of the formed image is deteriorated. Further, in some cases, additional problems arise such as a failure of the image-receiving sheet to be carried due to sticking of the image-receiving sheet to the thermal transfer sheet or sticking of the thermal transfer image-receiving sheet to a portion within the printer. Furthermore, also in the course of the production of the image-receiving sheet, discharge or a shock on the human body often occurs.
A conventional method for preventing electrification of the image-receiving sheet is to impart the function of preventing electrification to the printer itself. The effect, of preventing the electrification of the thermal transfer image-receiving sheet, attained by this method, however, is unsatisfactory. Another conventional method is to form an antistatic layer in the thermal transfer image-receiving sheet itself. The formation of the antistatic layer using a surfactant in the thermal transfer image-receiving sheet results in the development of sticking in the thermal transfer image-receiving sheet, thereby to cause a problem of blocking of the thermal transfer image-receiving sheet. This in turn causes problems such as deteriorated carriability of the thermal transfer image-receiving sheet within the printer and transfer of the antistatic agent onto the thermal transfer sheet at the time of printing, resulting in deteriorated antistatic effect.
Further, bleedout of the surfactant and the like unfavorably adversely affects color development of the dye and storage stability of the image. A resin-based antistatic layer is often formed as an intermediate layer between the dye-receptive layer and the substrate layer. In this case, the whiteness of the image-receiving sheet is disadvantageously deteriorated because the resin per se is colored. When a plastic sheet which is easily electrified, such as polyethylene terephthalate, is used as a core material, problems arise such as unsatisfactory antistatic effect.
Accordingly, an object of the present invention is to provide a thermal transfer image-receiving sheet which can exhibit high antistatic effect both before and after printing of an image by providing an antistatic layer in a laminated substrate layer in a thermal transfer image-receiving sheet comprising a laminated substrate layer, particularly including a plastic sheet.